1. Field of the Invention
The present invention relates to a method of training a recording medium reproduction equalizer and to a recording medium reproduction apparatus, and, in particular, to a recording medium reproduction apparatus including a read channel LSI or so applied for reading data recorded in a magnetic recording medium such as a hard disk or so, and to a method of training a so-called adaptive equalizer, so as to obtain equalization characteristics which are optimum upon reproducing digital data from an analog waveform read from the recording medium via a reproduction head in the above-mentioned recording medium reproduction apparatus.
2. Description of the Related Art
In case of decoding digital data from an analog signal read out from a recording medium in which the digital data is magnetically recorded, processing is performed such as to equalize the thus-obtained read signal into an equalization target according to a PR (partial response) technology as disclosed in U.S. Pat. No. 5,999,355 to Behrens et al. An equalizer applied for performing the above-mentioned equalization processing equalizes the read signal into the target PR characteristic through an adjustment control operation for predetermined coefficients of the equalizer performed according to a frequency characteristic of the read signal obtained via the reproduction.
As a method of adjusting the coefficient of the equalizer so as to adapt to the characteristic of the read signal each time with a reproduction apparatus such as a read channel LSI having the above-mentioned function (simply referred to as ‘training’, hereinafter), a so-called LMS (least mean square) algorism may be applied. However, in this method, in case a signal having a periodicity such as that from a preamble of a recording medium or so is processed, a result of the above-mentioned training may not converge into an optimum value but may rather diverge.
In order to avoid such a problematic situation, the training operation of the equalizer may be made ineffective for such a portion having a periodic pattern such as the preamble provided at the top of sectors in a hard disk which is a magnetic recording medium. Thereby, for the preamble, signal processing is performed only by means of an AGC (automatic gain control) loop by which the gain of the read signal is maintained at a constant value and a TR (timing recovery) loop by which a read timing in synchronization with the read signal is ensured.
Alternatively, as a method of performing the above-mentioned equalizer training operation at any time including a timing of handling a reproduction signal from the preamble, a method may be considered in which change in the coefficients occurring due to the training is restricted in a predetermined manner for the preamble. That is, according to this method, a restricting conditioning by which the equalization characteristics (gain and phase) are fixed is applied to the LMS method for a frequency of a sinusoidal wave of the read signal from the preamble. In this method, a variation vector of the coefficient vector is restricted onto a plane perpendicular to a signal vector (equalizer tap length) which is used as the restricting conditioning. Thereby, the frequency response to the signal vector for restricting conditioning is maintained at a fixed value. In other words, according to this method, the equalizer training is not substantially performed for the preamble.